Crystalline isomer of allethrin



Patented Aug. 19, 1952 CBYSTALLINE soMER F ALLETHRINV Milton S. Schechtcr, Washington, D. C., and Frederick B. La Forge-Arlington, Va.

1 No-Drawing. Application August 3, 1951,

Serial No. 240,262

n I (61. 260- 168) ,(Gianted under the act of March 3, 1883, as

11 Claims.

amended April 30, 1928; 370 0. G. 757) ALLETI-IRIN STEREOISOMERIC PRODUCTS AND PROCESSES The invention herein described may be manufactured and used by pr fer the Government of the United Statesof America for governmental purposesthroughout the world without the payment to us ofcany royalt thereon.

This invention relates to preparationof stereoisomeric products'from allethrin or allethrinlike compositions- We hereby dedicate the invention herein described to the free use of the people in the territory of the United States to take effect on the granting of a patent to us. I

In our prior applications Serial Numbers 75,282, filed February B, 1949; 161,481, filed May 11, 1950; and 168,142, filed June 14, 1950; we describe processes for synthesizing dl-2-allyl-4- hydroxy-3-methyl-2-cyclcpenten-1-one by ring closing the hydroxydiketone therein disclosed,

and for esterifying it with a synthetic racemic chrysanthemum carboxylic acid acylating agent to form an analogue of pyrethrins.

An object of this invention is to recover from allethrin, as it is produced by our syntheses, or by the syntheses: of others, a crystalline racemic form useful as a chemical and biological reference standard. c

When dl-2-allyl-4-hydroxy-3-methyl2-cyclopen-ten-l-one is acylated with a mixture of dicisand dl-trans-chrysanthemum monocarboxylic acid chlorides, as. disclosed in said prior applications, a very useful, highly insecticidal mix ture of esters is produced which has been named allethrin. Allethrin has a rapid knock-down effect and high killing power similar to the pyrethrins against housefiics and some other,

insects.

mercially. I

Allethrin, as so produced, is a mixture of eight isomers. To describe these-isomers, certain abbreviations will be employed as follows: dl 2- allyl-4-hydroxy-3-methyl-2-cyclcpenten 1 one will be calledv dl-allethrolone and its optically active forms will be called d-allethrolone and lallethrolone. The dl-cisand dl-trans-chrysanthemum monocarboxylic acids willybe called d1- cis-CMA and dl-trans-CMA respectively, and the optically active forms will be called d-cis-CMA, l-cis-CMA, d-trans-CMA and I-tranS CMA.

It is now beingfimanufactured com- The eightisomers present in designated as follows:

(a) d-Cis-CMA ester with d-allethrolone.

(b) d-Cis-CMA ester with l-allethrolone.

(c) l-Cis-CMA ester with d-allethrolone.

(d) l-Cis-CMA ester with l-allethrolone.

(e) d-Trans-CMA ester-with d-allethrolone.

(f) d-Trans-CMA ester with l-allethrolone.

(y) l-Trans-CMA ester with d-allethrolone;

(h) l-Trans-CMA ester with l-allethrolone.

Allethrin as produced commercially is optically inactive, hence, isomers a, b, c and d are present in equal amounts. Likewise, isomers e, f, g and h are present in equal amounts. However, since the dl-cis-CMA and dl-trans-CMA may not necessarilybe used'in equal amounts to prepare allethrin,=the total amount of esters .a, 12, o and. it may notbe equal to. the total amountyof esterste, f, g, and Hereinafter, a mixture of. equal amounts of esters a, b, c, and d will be called dl-cis-CMA ester with dl-allethrclone; a mixture of equal'amounts of esters e, f, and h will be called, dl-trans-CMA ester with 117311-- lethrolone.. i :1.-

After having'distilled some allethrin in a moallethrin may be lecular stillin order to purify'it, it was noticed that upon'cooling some to a' low temperature,

'about 15 C., in an acetone-Dry Ice bath, part of the allethrin crystallized. This crystallization was also efiected by cooling to a low temperature a concentrated'solutionof allethrin dissolved in solvents such aslow-boiling petroleum ether or The crystals were filtered off and isooctane. washed with cold isooctane :c'n afilter funnel which was kept cold by means of a. jacket filled with a cooling medium. The crystals. were recrystallized by dissolving in isooctane, cooling to a low temperature, filtering at 'a' low temperature and washing with cold isooctane. When'so purified, and dried, the colorless crystals had a melting point of -51 C.

This crystalline isomer of allethrin was shown to be an ester of dl-trans-CMA by saponification of the ester and identification of the dl-trans- CMA, as follows: 1 One gram. of this crystalline isomer was 'saponified by refluxing. with 20 ml. of 0.5 N ethanolic sodium hydroxide solution for one hour, the ethanolfiwaslargely removedby heating on the steam-bath and 'the'residuedis- 0 solved in water and-extracted with ether to remove neutral material. The aqueouslayerwas might crystallize out at very low temperatures,

melt before reaching room temperature.

The crystalline alpha-dl-transisomer ofallethrin has a high insecticidal activity and high knockdown power towards house flies and should serve as a useful biological reference standard in insecticidal tests such as in the Peet-Grady method of testing insecticides. For many years, a standardized solution of pyrethrins in purified kerosene, commonly referred to as the Official Test Insecticide of the Chemical Specialties ,Manufacturers Association, has been employed determination with authentic dl-trans-chrys anthemum monocarboxylic acid. It should be noted that dl-cis-chrysanthemum 'monocarboxylic acid melts much higher, i. e., at 1l5-116.

The crystalline isomer was again 'proven to be an ester of dl-trans-CMA by a second method of proof. The dl-allethrolone was acylated with the acid chlorides of dl-cis-CMA and (ll-trans- CMA and the respective esters were distilled in high vacuum. The dl-cis-CMA ester with dlallethrolone had a boiling point of 146-149 at 0.4 mm. and n 1.5070. The dl-trans-CMA ester with dl-allethrolone had a boiling point of 147- 150 at 0.4 mm. and n 'L5047. These esters were cooled and seeded with a few crystals of the crystalline isomer of M. P. 50-51 0. The dl-cis- CMA ester with dl-allethrolone could not thus be induced to crystallize but the dl-trans-CMA ester with dl-allethrolone did crystallize in part upon being cooled and seeded. The dl-trans-CMA ester with dl-allethrolone was dissolved in isooctane, cooled, seeded, and permitted to crystallize. The crystals were cold isooctane, and. dried; the melting point of the crystals was 50-5? C. There was no depression in a mixture melting point of the latter with the crystalline allethrin isomer originally obtained from allethrin.

Since only optically inactive or racemic forms can be crystallized from opticallyinactive allethrin or from the dl-trans-CMA'ester with dlallethrolone, the crystalline allethrin isomer M. P. 50-51 C. may consist isomers e and h, or of equal parts of isomers J and g. It should be possible to decide between these two alternatives by determining which pair (e and h or f and. g) of the individually prepared esters, e, j, g, and 71., would give a crystalline product identical with the crystalline isomer al-' ready isolated having a M. P. of 50-51". Until this is done, it is proposed that. the crystalline allerthrin isomer of M. P. 5051 which we have either of equal parts of filtered cold, washed with isolated be named the alpha-dl-trans-isomer of allethrin. The other opticallyv inactive isomer which would be found concentrated in the filtrate of the dl-trans-CMA ester with dl-allethrolone after the crystalline alpha-'dl-trans-isomer of allethrin had been removed, we propose to call the beta-dl-trans-isomer of allethrin. The dltrans-CMA ester with dl-allethrolone consists of equal parts of the alphaand beta-dl-transisomers of allethrin.

There are four optically inactive forms of allethrin isomers that might possibly'crystallize from allethrin, namely, the alpha-dl-trans-isomer of allethrin, the beta-dl-traris-isomer' of allethrin, and two corresponding dl-cis-isomers of allethrin. Although there is evidence that one or more of the other isomers of allethrin crystallize out when kept in concentrated isooctane solution in'an acetone-DryIcei-bath, only the'abovedescribed alpha-dl-trans-isomer of allethrin seems to have a melting point above room temperature, i. e. at -51. Such other isomers as at low temperature.

as a reference standard in Feet-Grady and other types of insecticide tests. There are diificulties in analyzing and standardizing the pyrethrins for such use because the pyrethrins are mixtures of at least four insecticidally active ingredients derived from natural sources. The alpha-dl-transisomer of allethrin can be obtained as a pure, crystalline substance and should serve as an excellent biological standard. It may also be useful as a pure standard for checking chemical analytical methods for substances of the pyrethrin or allethrin type. Further advantages of the crystalline compound are ease-of handling and shipping.

Another object of this invention is to increase the insecticidal activity of mixtures of allethrin isomers. Since the crystalline alpha-dl-tra'nsisomer of allethrin seems, 'according'to our tests, to have a somewhat lower toxicity toward-housefiies than either allethrin or the beta-dl tr'ansisomer of allethrin, it is possible to increasethe insecticidal activity of allethrin or of the dltrans-CMA ester with dl-allethrolone'by crystallizing out any alpha-dl-trans-isomer of allethrin and filtering it off from the ester mixtures} or from their solutions in a solvent such as isooctane,-

The preferred low temperature range for separating the crystalline alpha-dl-trans-isomer of allethrinv in our process is from about 10 Czdown' to about minus 40 C. v

Two examples of the preparation of crystalline alpha-dl-trans-isomer of allethrin areas follows:

EXAMPLE 1 About 60 g. of allethrin obtained as disclosed in our prior applications was'dissolved in about 60 m1. of isooctane and was cooled in the freezing compartment of a refrigerator. I After seed-' ing with a few crystals of the alpha -dl-transisomer of allethrin (obtained by cooling some allethrin dissolved in isooctane in an acetone- Dry Ice bath) it was allowed to stand in the freezing compartment about -15 C.) until crystallization was complete. The crystals were filtered off in a glass filter funnel having a sintered glass filter disc, the funnel being cooled by means of a cooling jacket filled with isooctane cooled to about minus 15 C. by the addition of Dry Ice from time to time. During the vacuum filtration, the crystals in the funnel'were'prm:

tected from moisture by means of a stopper carrying a calcium chloride-filled drying tube. The crystals were washed twice with small portions of isooctane which had been cooledinan acetone-Dry Ice bath. After drying in vacuo, the crystals weighed about 10.2 g'. and had M. P. 49-50. The crystals were recrystallized by dissolving in isooctane, cooling andzfiltering in thesame manner as described above: The pure. colorless 'alpha-dl-transrisomer of allethrin; crystals had a melting pointof- 505l and were analyzed afterr'having been dried in vacuo over;

phfifiphdrous' pento'xi-de in an Abderhalden dlier.

Analysis: calculated re ocuse C, 75.46%; H, 3.67%, Found: C, '75.41%';"I-I, 8.67%. 1

It will be noted that in 'Egample'l above the allethrin material employed contained the eight isomers' 'listed abOva b'eing a product prepared byfesterifying with the mixture of synthetic dlcisand dltran's-chrysanthemum "monocarboxylic acid halides.

"In the following Example '2, the material ein-' p'lo'yed" is prepared by esterym the' -cyclopentenolone with d1 --'trans" chrys'aihthenium monocarboxylic acid '"halide.""-"Consequently there are no dl-cis moieties-involved;

Eight andfour'tenthsgrams of'the til-trans- CMA ester with .dl-ralleth-rolone (which had a boiling point of 147-1502 at'0.4 'mnirandn'z l.5047),'prepared by the processes of ourprior applicationa'was. dissolved in 12.6 ml. of isooctane and was cooled in the freezing compartment of the refrigerator to about 15 C. :After seeding with afew crystals of the alpha-dl-trans isomer of allethrin it was allowed to' stand in the freezing compartment until crystallization was complete. The'crystals were filteredofi. in a glass filter funnel having a sinteredrglass filter disc,.the funnel being cooled by means of a cooling jacket filled with isooctane cooled to about minus 30 C. by the addition of Dry Ice from time to time. During the vacuum filtration, the crystals in the funnel were protected from moisture by means of a stopper carrying a calcium chloride-filled drying tube. The solvent was removed from the filtrate in vacuo leaving 4.4 g. of oil, n 1.5050. This oil consists almost entirely of the beta-dl-trans-isomer of allethrin with only about 5% of the alpha-dl-transisomer of allethrin dissolved in it, and is the substance referred to as the beta-dl-transisomer of allethrin in insecticidal tests in Tables I and II.

The crystalline portion was recrystallized from isooctane in the manner described in Ex-. ample 1 giving a product which had a melting point of 50-51" C. and which gaveno depression in a mixture melting point determination with the pure alpha-dl-trans-isomer of allethrin of Example 1.

This invention is not to be construed as being limited to the solvents and conditions described in the examples. Other solvents, temperatures, and modes of filtration or centrifugation may also be employed as should be evident to those skilled in the art.

Insecticidal tests of materials pertaining to this invention are given in Tables I and II. It is evident that although the alpha-dl-transisomer of allethrin is somewhat inferior to allethrin in tests against housefiies, the beta-d1- trans-isomer of allethrin is superior to allethrin. Since there is considerable specificity in biological tests with insecticides it is possible that the alpha-dl-thrans-isomer of allethrin might prove to be superior to allethrin against some species of insects other than houseflies.

The alpha-dl-transand beta-dl-trans-isomers of allethrin may be formulated for insecticidal or insect-repellent applications in various ways known to those skilled in the art, for use as dusts, sprays, aerosols, as emulsions, in kerosene,

I bea-dl-trans-Isomer of alle 3 Y 1 domestica);. by tu v Material ration? MgJmluelpha-dl-trens-Isomer ofjall 99 thrin, M. F. 60 519 c. alpha-dI-trans-Isomer oi thrin.M P 50 1C thrin, M. P, 5.0-51 C n. beta -dl-trans-lsomer of allebetafifi trans-Isomer of ailsbetacfl l -traiis-lsomer of alle i Pyrethr'ins. Pyrethrins P yi-ethrins Pyrethrins.

1 Solutions were prep afed ln refined kerosene (Deobase). 2 Results are the average cf four tests atea'chppncentration. Table II .E1Tectioengss "d'yciins't fho u 's e' mes (Musca domesticaj of 'spr s containino alphadl tnmsand betct dltfans -is'omeis of Lillethrin. All matcrials'wefe 'tcsted at a, ame tmtion of 12 mg/ml. ivtfeflnedj kerosene (Deobase). Results are the averagew four tests each by the Feet-Grady method Knockdown Kill in Material 5 10 one Day minutes minutes Percent Percent Percent alpha-dl-trans-Isomcr oi allethrin, 68 90 M. P. 05l C. beta-dl-trans-Isomer of allethrin..- 95 99 74 Allethrln 94 99 63 Pyrethrins 96 99 38 or in other organic solvents. They may also be Having thus described our invention, we claim:

1. A process comprising cooling to below about 10 vC. the esters of dl-2-allyl-4-hydroxy-3- methyl-2-cyclopenten-1-one with dl-chrysanthemum monocarboxylic acid, the dl-chrysan'themum acid being at least in part the trans acid, to crystallize the alpha-dl-trans-isomer, namely,

the dl-trans-chrysanthemum monocarboxylic.

acid ester of said hydroxycyclopentenone, having a melting point when purified of about 5051 C., and separating the crystals. 7

2. A process comprising cooling to below about 10 C. dl-trans-chrysanthemum monocarboxylic acid esters of dl-2-a-llyl-4-hydroxy3-methyl-2- cyclopenten-l-one dissolved in an inert organic liquid solvent to crystallize out the alpha-d1- trans-isomer of allethrin having a melting point of about 50--51 C. when purified, removing the crystals, and thereafter distilling off the solvent leaving a residual oil comprising beta-dl-transisomer of allethrin. I

3. Crystalline dl-trans-chrysanthemum monocarboxylic acid ester of dl-2-allyl-4-hydroxy-3- methyl-2-cyclopenten-1-one having a melting point of about 50-51 C.

4. A process comprising cooling a composition essentially consisting of (11-015 and. dl-transchrysanthemum monocarboxylic acid esters of d1- 2 allyl 4 hydroxy-3-methyl-2-cyclopenten-l- 7 one, to a temperature below room temperature to crystallize the dl-trans-chrysanthemum monocarboxylic acid ester of dl-2-allyl-4-hydroxy-3- methyl-2-cyclopenten-l-one, said esters having a melting point of about 50-51 C. when purified, and separating the crystals.

5. A process comprising cooling a mixture of d1- cis and dl-trans-chrysanthemum monocarboxylic acid esters of dl-2-allyl-4-hydroxy- 3-methyl-2- cyclopenten-l-one, dissolved inian' inert organic solvent to a. temperature below roo'm temperature to crystallize the dl-trans-chrysa'ntheinum monocarboxylic acid ester of dl-2 allyl-4-hydroxy-3- methyl-2-cyclopenten-l-one, said ester having a melting point of about 50-51 C. when purified, and separating the crystals, said solution of the mixture being seeded with crystals of said ester;

6. A process comprising cooling a mixture ,of dl-cis and dl-trans-chrysanthemum monocar boxylic acid esters of dl-2-allyl-4-hydroxy-3- methyl-2-cyclopenten-1-one, to a temperature sufliciently below room temperature to crystallize the dl-trans-chrysanthemum monocarboxylic acid ester of dl-2-allyl-4-hydroxy-3-methyl-2- cyclopenten-l-one, said ester having a melting point of about 50-51 C. when purified, and separating the crystals, said cooling being in the range of plus 10C. to minus 40 C. I g y "I. A process comprising cooling a mixture of dl-cisand dl-trans-chrysanthemum vmonocarboxylic acid esters of dl- 2-allyl-4ehydroxy-3- methyl-2-cyclopentene1eone, dissolved in isooctane, to a temperature sufiiciently below room temperature to crystallize the dl-trans-chrysanthemum monocarboxylic acid ester of dl-2-al1yl- 4-hydroxy-3-methyl-2-cyclopenten-1 one, said ester having a melting point of about 50-51 C. when purified, and separating the crystals, the cooling being to a temperature in the range minus 15 C. to minus 40 C., the crystals being removed from the cold solvent and recrystallized from isooctane.

8. A process comprising cooling a composition essentially consisting of dl-cisand dl-transchrysanthemum monocarboxylic acid esters of d1- 2 allyl 4 hydroxy-3-methyl-2-cyclopenten-lone, dissolved in an inert liquid hydrocarbon solvent to a temperaturebelow room temperature to crystallize the dl-trans-chrysanthemum mono carboxylic acid ester ofv dl-2-allyl-4-hydroxy-3- methyl-2-cyclopenten-1-one,said ester having a melting point of about 50-51 C. when purified, and separating the crystals, said solution having been seeded with crystals of said ester.

9. The process of claim 8 in which the solvent is isooctane. V

10. The process of claim 2 in which the solvent is taken from the group consisting of isooctane and low boiling petroleum ether.

11. The process of claim 2 in which the solvent is isooctane.

' MILTON S. SCHECHTER.

FREDERICK B. LA FORGE.

No references cited. 

1. A PROCESS COMPRISING COOLING THE BELOW ABOUT 10* C. THE ESTERS OF DI-2ALLYL-4-HYDROXY-3METHYL-2-CYCLOPENTEN-1ONE WITH DL-CHRYSANTHEMUM MONOCARBOXYLIC AID, THE DL-CHRYSANTHEMUM ACID BEING AT LEAST IN PART THE TRANS ACID, TO CRYSTALLIZE THE ALPHA-DL-TRANS-ISOMER, NAMELY, THE DL-TRANS-CHRYSANTHEMUM MONOCARBOXYLIC ACID ESTER OF SAID HYDROXYCYCLOPENTENONE, HAVING A MELTING POINT WHEN PURIFIED OF ABOUT 50-51* C., AND SEPARATING THE CRYSTALS. 